Bias ply tires are conventionally made in a single stage process on a cylindrical mandrel. The plies of rubberized fabric, reinforcing cord and tire tread are all applied in proper order to the mandrel while it rotates and the cylindrical tire body so formed is then shaped in a steam press. Radial tires cannot be built up in that manner because the reinforcing cords or wires run more or less longitudinally of the mandrel and are laid on a substantially inextensible breaker band or belt. There are two commercial methods of making radial tires, called the single stage and the two-stage process respectively.
In the single stage process the underlying tire body is built up on a cylindrical, but expansible, rotating mandrel, the mandrel is then expanded in its central portion, generally by moving its ends toward each other, so as to convert the cylindrical tire body into a torus, and the breaker band, cords and tread are applied to that torus. A single stage machine and the process of tire building employing it are described in Cantarutti U.S. Pat. No. 3,560,301. In the two-stage process, with which this invention is concerned, the underlying tire body is built up on a cylindrical mandrel. The reinforcing cords, tread and breaker band are built up as a separate torus. The underlying body is then transferred to a tire shaping machine which expands the cylindrical body in its central portion in the way previously mentioned, the expanded torus is slipped over the underlying tire body before it is expanded, and the latter is then expanded against the cord and tread torus.
The first stage of the two-stage radial tire building process as generally practiced is quite similar to the corresponding portion of bias ply tire building, which is set out, for example, in Cantarutti U.S. Pat. No. 3,438,832. The ends of the plies which overlie the ends of the mandrel are turned down, the bead ring is applied thereto and the ply ends are turned up around the rings and over against the underlying plies by air-inflated double bladder assemblies at each end of the machine. These bladders inflate rapidly and actually snap the ply ends against the underlying tire body. This is done with the mandrel stationary. After the bladders have been retracted, the mandrel is rotated and stitcher wheels, also shown in the Cantarutti patent, which travel from the center of the mandrel outwardly toward each end, are utilized to press the ply ends against the underlying plies in a spiral pattern as the mandrel rotates. Sidewall stock is manually applied to the mandrel while it rotates, and is stitched with the same stitcher wheels.
In the single stage process, the ply ends are turned up around the bead rings by an inflatable double bladder assembly at each end like those used in bias ply tire building machines and in the first stage of two-stage radial tire building. However, those bladder assemblies are rotatable. The sidewall stock is laid out on the collapsed bladder assemblies while they are rotated, and is applied to the torus by inflating the bladders, thus lifting the sidewall stock and carrying it against the side of the torus, which is only a few degrees from vertical. Because of the relatively upright position of the torus wall, the bladders do not have to move any great distance axially of the mandrel. It is additionally advantageous to carry out this operation while the mandrel and bladder assemblies are both rotating, as the centrifugal force of rotation assists the air pressure throwing the bladders up against the torus. The sidewalls are then usually stitched mechanically to the torus by stitcher wheels.
A bias ply tire building machine does not require an expansible mandrel, but the mandrel of a tire building machine for radial tires by the single stage process, must be expansible. This expansion is conventionally accomplished by causing the mandrel ends to approach each other, so bulging the mandrel central portion. It has been found that in applying sidewall stock to the tire body in the single stage process on such a mandrel in the way outlined above, the stock tends to creep, and furthermore air bubbles are sometimes entrapped between sidewall stock and the underlying plies.